Vibrocompaction is an attractive process for the manufacture of nuclear fuels for fast reactors. The process can involve the high energy breakdown of irregular fuel particles within the fuel pins or, alternatively, a coarse fraction of fuel particles can be vibrated into its optimum packing arrangement using low energy vibration and a second component infiltrated into the spaces between the large particles once again using low energy vibration.
The second process is very attractive if the two components can be simply weighed and then packed to a predictable length within the pin but the success of the second process depends upon the particles which are infiltrated into the spaces between the large particles being of the correct size and shape. The infiltration of fines is reliant upon the small number of holes at the top of the coarse fuel column remaining open until all the fine particles have moved into position and only a small quantity of incorrect particles are needed to block the column and stop or severely reduce the rate of infiltration. Unfortunately current manufacturing processes do not always produce fine particles which can be guaranteed to infiltrate into position. In the instance of non-spherical fine particles, needles and flat particles can pass through existing sieves and in the instance of spherical gel-precipitation type fine particles, units of 2 to 6 particles can be linked together in a string and yet be able to pass axially through existing sieves. Furthermore, in both types of fine particles, fibres, brush hairs and other plant debris passes through the fine sieves and into the product. In addition to the normal sieving operations, therefore, means is needed which will effectively prevent undesirably shaped particles and debris from getting into the fine particle product. The present invention seeks to provide such means.